The present invention relates to a shifting device for a transmission unit of a vehicle, in particular a vehicle that is driven by muscle force, having a first shaft, which is formed as a hollow shaft, on which a plurality of free gears is mounted, wherein the free gears are in engagement with a corresponding plurality of gearwheels, which are mounted on a second shaft, wherein the free gears are connectable to the first shaft by means of selecting means, wherein the selecting means can be actuated by means of a camshaft arranged coaxially in the first shaft, wherein the camshaft is connected to driving means in order to be rotated relative to the first shaft to actuate the selecting means.
The present invention furthermore relates to a gear unit for a vehicle, in particular a vehicle that is driven by muscle force, having a first shaft, on which a plurality of first gearwheels is mounted, a second shaft, on which a corresponding plurality of second gearwheels is mounted, wherein the second gearwheels are in engagement with the corresponding first gearwheels.
The present invention furthermore relates to a vehicle having a frame and a gear unit, which has a first shaft, on which a plurality of first gearwheels is mounted, and a second shaft, on which a corresponding plurality of second gearwheels is mounted, wherein the second gearwheels are in engagement with the first gearwheels, wherein the first and the second shaft are mounted in a gear case which at least partially surrounds the gear unit.
Gear units of this kind are used to provide different transmission ratios for driving a vehicle, in particular a vehicle that is driven by muscle power.
There are fundamentally three types of gear shift for vehicles or bicycles driven by muscle power, namely derailleurs, hub gears and bicycle transmissions.
The derailleur has remained essentially unchanged in the last few decades. In this case, a chain transmits the motive power from a crank to the rear axle of the bicycle, and a set of sprockets comprising up to 11 sprockets is mounted on the rear axle, between which it is possible to shift by means of a frame-mounted derailleur for controlling the chain. Moreover, most bicycles are additionally fitted with a shift mechanism at the chain wheel associated with the bottom bracket. In this case, up to three chain wheels are mounted on the crank, and it is possible to shift between them by means of a front derailleur attached to the frame. Derailleurs of this kind provide up to 30 gears, although, by the nature of the system, many of the gears are redundant and some gears are of limited or no use due to high frictional losses caused by diagonal chain alignment.
The disadvantage with the derailleur principle is that, in addition to the large number of redundant gears and the frictional losses, the components are exposed and are therefore directly subject to environmental influences such as water and dirt and can very easily be damaged by impact.
The second type of commercially available bicycle shift mechanism is the hub gear. In contrast to the derailleur, this is understood to mean a gear mechanism built into the hub casing of the rear axle. A hub gear generally has no external shift components and is therefore not susceptible to impact and less exposed to environmental influences than the derailleur. A hub gear of the kind known from DE 197 20 794 A1, for example, can currently provide up to 14 gears. The disadvantage with the principle of the hub gear in the rear axle is that the weight of the rotating masses is increased, and, in the case of bicycles with rear wheel suspension, that the unsprung mass relative to the total weight is increased. Moreover, the center of gravity of the bicycle shifts in the direction of the rear axle, and this has a disadvantageous effect on the ride characteristics of the bicycle, especially in the case of mountain bikes with rear wheel suspension.
A hub gear of this kind is known from EP 0 383 350 B1, for example, in which two planetary mechanisms are arranged coaxially with a hub fixed with respect to a housing, wherein the input shaft can be connected to planet carriers, and the sun gears of the planetary mechanism can be connected for conjoint rotation, by means of a rotatable shifting device, to the hub fixed with respect to the housing in order to provide different transmission ratios in the overall gear mechanism. The disadvantage with this gear mechanism is that the construction of the overall gear mechanism is complex and is therefore, on the one hand, expensive to produce and, on the other hand, has a high weight due to the large number of components while providing only a small number of achievable gears.
The third variant of bicycle shift mechanisms are the bicycle transmissions mounted in the region of the bottom bracket or bottom bracket transmissions. This type of bicycle shift mechanism is never or only very rarely found on commercially available bicycles. In general, bicycle transmissions of this kind have the advantage over conventional derailleurs or hub gears that they do not have any exposed components and are therefore protected from impact and environmental influences, and furthermore shift the center of gravity of the bicycle to the center while, at the same time, reducing the total unsprung mass. This is particularly advantageous in mountain bike sport. One technical challenge with bicycle transmissions of this kind is to provide a compact construction combined with a large number of selectable gears.
U.S. Pat. No. 5,924,950 A discloses a bicycle transmission having an input shaft, on which a plurality of drive gears is mounted, and a countershaft, on which a corresponding number of selectable driven gears is mounted. The selectable gears on the countershaft are selected by means of a plurality of axially movable shift pins and freewheels arranged in the countershaft, wherein the countershaft is connected to a pinion as an output member of the vehicle transmission via a planetary mechanism. The pinion is connected to the sun gear of the planetary mechanism via a clutch, and the annulus of the planetary mechanism can be braked by means of a Bowden cable. By means of this bicycle transmission, it is possible to obtain 14 gears. The disadvantage with this system is the large axial extent of the design and the relatively small number of gears that can be obtained, namely 14.
WO 2008/089932 A1 furthermore discloses a gear unit for bicycles, in which a high number of gears can be obtained using two countershafts and an additional transmission subsection, by multiplying the individual gears of the two transmission subsections, and, at the same time, a compact construction can be achieved. The disadvantage with this gear unit is that a camshaft is moved axially to select the free gears and, as a result, the axial extent of the transmission design is great.
EP 1 982 913 A1 discloses a transmission for bicycles in which free gears are mounted on an input shaft of the transmission and can be connected selectively to the input shaft by means of a sleeve mounted in the shaft, wherein the sleeve is turned relative to the input shaft by means of two planetary mechanisms in order to select the free gears. The planetary mechanisms are arranged coaxially with the input shaft and are actuated by means of a selector shaft, which is offset parallel to the input shaft and is connected to a Bowden cable. The selector shaft is connected for conjoint rotation to a planet carrier of one of the planetary mechanisms by a spur gear mechanism in order to transmit the rotation of the selector shaft to the sleeve. The disadvantage with this transmission is that the additional rotation is transmitted to the planetary mechanism by means of the selector shaft which is offset in parallel, thereby requiring a large amount of installation space for the gear unit.